4U1957+115
Black hole (BH) spin measurements in X-ray binaries (XBs) are crucial for understanding BH formation, but current techniques face significant limitations due to spectral complexity and the transient nature of most systems. In particular, relativistic reflection measurements suffer from uncertainties related to unresolved narrow features and continuum modeling, especially in low-mass XBs (LMXBs), which are only rarely observable, during outbursts. We propose a 50 ks XRISM observation of 4U 1957+115 - the only persistent BH LMXB - to detect and characterize narrow features in the Fe band. This will quantify their impact on spin measurements and test for a tentative ultra-fast outflow. The results will improve reflection modeling and refine spin estimates across the BH population.
obsid = 202036010 / Unique Observation/Sequence Number
object = 4U1957+115 / Object name
pi_name = DRAGHIS PAUL / Proposal Principal Investigator Name
ra = 299.850384043293 / Right Ascension (Pointing Position) (deg)
dec = 11.7086676045812 / Declination (Pointing Position) (deg)
roll_angle = 241.11243852703 / Roll Angle (deg)
start_time = 2025-11-24T01:20:04 / Start Time of the Observation
stop_time = 2025-11-25T08:43:04 / Stop Time of the Observation
exposure = 62206.915481 / Effective Total Observation Exposure (s)
public_date= 2026-12-03 / Public Date